1. Field of the Invention
The present invention relates to a process and processor for reusing a waste paint discharged from processes such as coating process of applying paint to a vehicle body.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
For instance, in a paint shop, a vehicle body is painted out by spraying coatings in a paint booth. In spraying coatings, there is some coating liquid which is not adsorbed onto the vehicle body due to spray missing (overspray). The missing spray coating enters into circulating water in a pit on the lower side of the booth, and is led to a settling (precipitation, deposit) tank together with the water. After some time period, soft cake-like masses settle and these are collected as waste paints. The waste paint is burnt up, or otherwise is dried and ground as a processed waste paint which is generally used for asphalt sheets and chipping resistant coatings.
However, the waste paint collected in the paint booth is not cured because it is not passed through a curing process. Therefore it is necessary to completely cure the waste paint to pulverize it for its reuse.
Examples of processors for drying and pulverizing the waste paint include a screw drying machine, a stirring drying machine and a rolling drying machine. Methods for processing the waste paint by using each of the drying machines are explained in order.
FIG. 5 is a schematic view for explaining a method for processing the waste paint by using the screw drying machine. In this process, the waste paint placed in a hopper 101 is introduced into a screw dryer 105 by a screw conveyor 102 and a belt conveyor 103, and dried in the screw dryer 105 to be pulverized, whereby the waste paint can be converted into resources.
The screw dryer 105 is provided with a cylindrical processing tank 106 into which the paint waste is introduced by the belt conveyor 103, a rotating grinding rotor 107 having plural grinding rotors 107b mounted on a rotating axis 107a which is horizontally extended in a processing tank 106, and a screw conveyor 108 disposed on the lower side of the processing tank 106.
When the waste paint is introduced into the processing tank 106, the grinding of the waste paint is started by rotation of the rotating grinding rotor 107, and simultaneously its heating is started by steam. In the process of heating of the waste paint, the waste paint is melted to form a large mass having high viscosity (e.g., heated rice cakes). In this condition, the heating promotes the vaporization of a solvent in the waste paint to dry out the waste paint.
When the waste paint is heated, the curing of a resin component in the waste paint is proceeded, and as a result the cured waste paint is ground with the rotating grinding rotor 107. The ground waste paint (i.e., resin powder) is fed as resources from the lower side of the processing tank 106 by the screw conveyor 108.
On the other hand, the water and solvent contained in the waste paint are vaporized in the processing tank 106, and the vaporized water and solvent are liquefied or condensed by a heat exchanger 109 to be discharged as condensed liquid. In this case, hydrocarbon is removed and only nontoxic gas is discharged. A reference number 109a is a vacuum pump for reducing pressure in the heat exchanger 109.
FIG. 6 is a schematic view for explaining a method for processing the waste paint by using the stirring and drying machine. The waste paint placed in a hopper 101 is introduced into the stirring dryer 115 by a screw conveyor 102 and a belt conveyor 103, and dried in the stirring dryer 115 to be pulverized, whereby the waste paint is converted into resources.
The stirring dryer 115 is provided with a cylindrical processing tank 116 having a bottom into which the paint waste is introduced, a rotating grinding rotor (grinder) 117 with grinding rotors 117b mounted on a rotating axis 117a which is perpendicularly extended in the processing tank 116, and an outlet 118 disposed on the lower side of the processing tank 116.
When the waste paint is introduced into the processing tank 116, grinding of the waste paint is started by rotation of the rotating and grinding rotor 117, and simultaneously its heating is started by the steam. In the course of heating the waste paint, the waste paint is melted to form large masses having high viscosity (e.g., heated rice cakes). In this condition, the heating promotes the vaporization of a solvent in the waste paint to dry out the waste paint.
When the waste paint is heated, the curing of a resin component in the waste paint is proceeded, and as a result the cured waste paint is ground by the grinding rotor 117. The ground waste paint (i.e., resin powder) is fed as resources from the outlet 118 provided on the lower of the processing tank 116.
Water and solvent contained in the waste paint are vaporized in the processing tank 116, and the vaporized water and solvent are liquefied or condensed by a heat exchanger 109 to form condensed liquid, and hydrocarbon is removed to discharge only nontoxic gas into atmosphere.
FIG. 7 is a schematic view for explaining a method for processing the waste paint waste by using the rolling drying machine. The waste paint placed in a hopper 101 is introduced into the rolling dryer 121 by a screw conveyor 102 and a belt conveyor 103, and similarly dried in the rolling dryer 121 to be pulverized, whereby the waste paint is converted into resources.
The rolling dryer 121 is provided with a box-shaped processing tank 122 into which the waste paint is introduced, a pair of rotating drums 123 which are horizontally disposed opposite to each other in the processing tank 122 and which rotate in the opposite direction each other, a scraper blade 124 whose edge is contact with the surface of each of the drums 123, and a screw conveyor 125 disposed on the lower side of the processing tank 122.
A large mass of waste paint, which is introduced from the upper side of a processing tank 122, is fed between a pair of rotating drums 123 opposite to each other, rolled therebetween under heating, whereby drying and grinding are started. The rolled and dried waste paint is adhered in the form of sheet onto the surface of the rotating drums 123 to be moved by rotation of the drums, and scratched up by the scraper blade 124. The scratched waste paint is fallen from the drums 123 and fed as resources from the lower side of the processing tank 121 by the screw conveyor 125.
Water and solvent contained in the waste paint are vaporized in the processing tank 121, and the vaporized water and solvent are liquefied or condensed by a heat exchanger 109 in the same manner as the screw drying machine 100, and hydrocarbon is removed to discharge only the nontoxic gas into the atmosphere.
According to a method for processing the waste paint using the screw drying machine shown in FIG. 5, the collected waste paint is stirred under heating with the rotating grinding rotor 107 within the processing tank 106 and therefore it is gradually cured. In the beginning stage of the curing, the waste paint is increased in viscosity to become high viscous (such as in the condition of heated rice cake), and therefore resistance to rotating of the rotating grinding rotor 107 is increased and subsequently power for driving the rotor (e.g., consumed power of electric motor) is also increasingly required. For the reason, it is required to switch the rotation number (speed) of the rotating grinding rotor 107 to a low rate and much time is taken for reduction of water content of the waste paint.
Also in the method for processing the waste paint using the stirring and drying machine shown in FIG. 6, the collected waste paint is stirred under heating with the rotating grinding rotor 117 within the processing tank 116 and therefore it is gradually cured. In the beginning stage of the curing, the waste paint is increased in viscosity to become high viscous (such as in the condition of heated rice cake), and therefore the resistance to rotation of the rotating grinding rotor 117 is increased and subsequently the power for driving the rotor (e.g., consumed power of electric motor) is also increasingly required. For the reason, it is required to switch the speed of the rotating grinding rotor 117 to a low rate and much time is taken for reduction of the water content of the waste paint. Further, it is particularly difficult to conduct continuously the steps of from a step of introduction of the waste paint into the processing tank 116 to a step for drying thereof, and therefore a working step for reserving the waste paint is required to reduce the working efficiency.
According to a method for processing the waste paint using a rolling and drying machine shown in FIG. 7, the collected waste paint is rolled and heated between a pair of rotating drums 123 opposite to each other to be dried. However, much time is taken for obtaining waste paint having low water content suitable for resources by the rolling and dehydrating/drying by the use of the rotating drums 123 and therefore it is difficult to successfully perform the method.
The method for processing waste paint using the screw, stirring or rolling drying machine requires much time and cost for processing the waste paint. Hence, a method for processing efficiently the waste paint is desired
As a result of many experiments, it was found that, in the drying stage of the waste paint by the stirring dryer, there are some relationships among variations of characteristics of the waste paint, variation of stirring power, variation of temperature of the waste paint and variation of the water content.
The experiment was carried out as follows: 8 kg of the waste paint having 30% by weight of water content was dried using a stirring dryer of volume of 20 L under the conditions of steam pressure of 5 kg/cm3. As a result, the drying characteristics of the waste paint are shown in FIG. 8.
The drying characteristics of the waste paint of FIG. 8 indicate the followings: In the beginning stage of the curing of the waste paint by rotating the grinding rotor and by drying by heat, value of electric current for driving the rotor is rapidly increased due to high viscosity of the waste paint, and simultaneously the content of water in the waste paint is drastically reduced whereby the waste paint is made in critical state to be destroyed. As a result, the current value is suddenly lowered because of reduction of load of the electric motor, and then the current value is approximately kept in constant while the water content is gradually reduced. Hence, it is understood that the beginning stage of the curing using the waste paint having relative high content of the water requires high power.
On the other hand, the rolling dryer rolls the waste paint between a pair of rotating drums and therefore it is difficult to sufficiently reduce the content of water after the processing by rolling. However, it has been confirmed by the experiments that the continuous rolling of the waste paint enables efficient drying (dehydration) in the beginning stage in a short time by a relative low power.
In view of the above-mentioned drying characteristics of the stirring dryer and rolling dryer, an object of the invention is to provide a process and processor for reusing waste paint (i.e., a process and processor for converting waste paint into resources) which bring about highly efficient processing of the waste paint.
The present invention to attain the object is provided by a process for reusing a waste paint comprising:
rolling the waste paint between a pair of heated rotating drums disposed opposite to each other for dehydrating and drying the waste paint (a rough drying step),
accumulating successively the dehydrated and dried waste paint in a processing tank with the accumulated waste paint being stirred with a rotating grinding rotor in the processing tank under cooling (a holding step), and
drying and pulverizing the accumulated waste paint with the rotating grinding rotor under heating (a main drying step).
According to the above-mentioned invention (corresponding to claim 1), the rough drying step includes heating and dehydrating/drying waste paint having relative high content of water by rolling it between a pair of heated rotating drums. In the rough drying by the use of the rotating drums, power for dehydrating and drying the waste paint is extremely low, and further the characteristics of thermoset resin of the waste paint are destroyed. The waste paint dried in the rough drying step is cooled in the holding step, and stirred with the rotating grinding rotor to be successively accumulated in the state free from fusing and aggregation each other.
In the main drying step, the waste paint accumulated in the holding step is dried and pulverized with the rotating grinding rotor in the processing tank to provide resources. The waste paint in the main drying step can be easily and efficiently pulverized with the rotating grinding rotor in less power because the characteristics of thermoset resin of the waste paint in the rough drying step is destroyed and the waste paint is accumulated successively in the state free from fusing and aggregation each other.
Thus, it is possible that the above-mentioned process for reusing a waste paint provides pulverized waste paint suitable for resources from waste paint in extremely reduced energy, and converts easily and efficiently the waste paint into resource.
Another invention to attain the object is provided by a processor for reusing a waste paint comprising:
a rolling dryer comprising a pair of heatable rotating drums disposed opposite to each other for rolling the waste paint introduced therebetween to dehydrate and dry the waste paint,
a stirring dryer for holding the waste paint comprising a processing tank configured for cooling and successively accumulating the dehydrated and dried waste paint therein and a rotating grinding rotor for stirring the accumulated waste paint in the processing tank under cooling, and
a stirring dryer for main drying comprising a heatable processing tank for heating the accumulated waste paint and a rotating grinding rotor therein for pulverizing and drying the accumulated waste paint under heating.
According to the above-mentioned invention (corresponding to claim 2), the processor comprising the rolling dryer that heats and dehydrates/dries waste paint having relative high content of water by rolling it between a pair of heated rotating drums and further destroys the characteristics of thermoset resin of the waste paint; a stirring dryer for holding that stirs the roughly dried waste paint under cooling to accumulate it in the state free from fusing and aggregation each other; and the stirring dryer for main drying that pulverizes and dries the accumulated waste paint with the rotating grinding rotor under heating to provide resources, permits the above-mentioned process for reusing a waste paint (claim 1) to advantageously perform.
The further invention to attain the object is provided by a processor for reusing a waste paint comprising:
a rolling dryer comprising a pair of heatable rotating drums disposed opposite to each other for rolling the waste paint introduced therebetween to dehydrate and dry the waste paint, and
a stirring dryer comprising a processing tank capable of regulating temperature provided with temperature-regulating means and a rotating grinding rotor for successively accumulating the dehydrated and dried waste paint therein, for stirring the accumulated waste paint by a rotating grinding rotor under cooling by the temperature-regulating means, and for pulverizing and drying the accumulated waste under heating by the temperature-regulating means.
According to the above-mentioned invention (corresponding to claim 3), the processor comprising the rolling dryer that heats and dehydrates/dries waste paint having relative high content of water by rolling it between a pair of heated rotating drums; a stirring dryer that stirs the roughly dried waste paint under cooling to accumulate it in the state free from fusing and aggregation each other (a holding step) and that pulverizes and dries the accumulated waste paint with the rotating grinding rotor under heating to provide resources (a main drying step), permits the above mentioned process for reusing a waste paint (claim 1) to advantageously perform. Moreover, since only one stirring dryer performs both of the holding step and the main drying step, the processor for reusing a waste paint can be simplified and compactified compared with the processor described in another invention (claim 2).
The further invention to attain the object is provided by a processor for reusing a waste paint comprising:
a rolling dryer comprising a pair of heatable rotating drums disposed opposite to each other for rolling the waste paint introduced therebetween to dehydrate and dry the waste paint,
plural stirring dryers comprising a processing tank capable of regulating temperature provided with temperature-regulating means and a rotating grinding rotor for successively accumulating the dehydrated and dried waste paint therein, for stirring the accumulated waste paint by a rotating grinding rotor under cooling by the temperature-regulating means, and for pulverizing and drying the accumulated waste under heating by the temperature-regulating means, and
conveyor means comprising a conveyor rout and means for changing the conveyor rout disposed between the rolling dryer and each of the stirring dryers, the waste paint dried in the rolling dryer being fed to each of the stirring dryers by changing the conveyor rout (by the means for changing the conveyor rout),
wherein the means for changing the conveyor rout is switched such that at least one of the plural stirring dryers conducts a step comprising accumulating successively the dehydrated and dried waste paint and stirring the accumulated waste paint with a rotating grinding rotor under cooling, and the waste paint dried in the rolling dryer is fed to the stirring dryer to conduct the step.
According to the above-mentioned invention (corresponding to claim 4), the processor includes the rolling dryer, the plural stirring dryers for successively accumulating the dehydrated and dried waste paint and stirring the accumulated waste paint under cooling (a holding step), and for pulverizing and drying the accumulated waste under heating (a main drying step), and the conveyor means feeding the waste paint dried in the rolling dryer to each of the stirring dryers by changing the conveyor rout. In the processor, the waste paint dried in the rolling dryer is fed to the stirring dryer in order of precedence to conduct the above step, whereby the rolling dryer can be continuously operated to efficiently convert the waste paint to resources.
In the processor for reusing a waste paint (corresponding to claim 3 or 4), the temperature-regulating means has a jacket provided around the processing tank of the stirring dryer, and switching means for feeding one of cooling water and steam to the jacket.
According to the above-mentioned invention (corresponding to claim 5), the waste paint in the processing tank can be efficiently heated or cooled by feeding one of cooling water and steam to the jacket provided around the processing tank by switching.